a conceptual primer
One can say that the concept of a game is a concept with blurred edges.—‘But is a blurred concept a concept at all?’—Is a photograph that is not sharp a picture of a person at all? Is it even always an advantage to replace a picture that is not sharp with one that is? Isn’t one that isn’t sharp often just what we need?
Frege compares a concept to a region, and says that a region without clear boundaries can’t be called a region at all. This presumably means that we can’t do anything with it.
—Ludwig Wittgenstein (Philosophical Investigations, trans. G.E.M. Anscombe et al., §71)